1. Field of the Invention
The invention relates to a method for displaying images and to a display system, in particular for medical images, for example, digital mammograms.
2. Prior Art
In the course of mammogram-screening for the purpose of preventing breast cancer, mammograms are taken in periodic intervals for all women of a specific target group and examined for suspicious circumstances. In each examination, an image of each breast is routinely taken from above (craniocaudal, CC) and from the side (mediolateral oblique, MLO). These four mammograms are usually compared with the four images of the preliminary examination, so that the radiologist, as a rule, must view eight mammograms for each case. Additionally, it can be desirable in displaying computer generated mammograms to, for instance, synthetically increase the contrast of some of the images in order to more clearly display suspicious structures.
The radiologist has only a short time for the examination of this multitude of images. A well trained radiologist is able to examine about 100 cases per hour. The reliable assessment of eight or more exposures in such a short time is then only possible if they are consistently presented to the radiologist in the same, familiar form and possibly existing additional views or images (also images of other modalities, for example, ultrasound images or MR-Mammograms) are quickly available.
The radiologist uses a special screening-analysis station for digital mammogram screening that generally consists of a high power computer with two high resolution monitors and special input apparatus for controlling the system. The monitors of such a system must be able to display at least 2000×2000 pixels with a grayscale depth of 8 or 10 bits/pixel. In spite of this high resolution, the digital mammograms, which consist of 4000×4000 pixels or more, must be scaled down for display or must be examined in parts.
In support of a fluid workflow, an analysis station offers several standardized arrangements of images on the monitors, whereby each monitor can be subdivided into two or four sub-windows. Typical examples of such arrangements are displayed in FIG. 1.
The possible arrangements, as well as the sequence in which the radiologist will view them, are for the most part configurable. Beyond these standard arrangements, the radiologist must have the capability to be able to display all available images in arbitrary arrangements. For example, a comparison can require the display of the current CC-image of a breast on the left and the corresponding image of the preliminary examination on the right, although this arrangement is not provided in the system configuration. Therefore, the manual arrangement of the individual images must be able to occur quickly and is allowed only a minimal interaction complexity in order to not hold up the work flow.
There already exist varied programs that have the ability to display several digital images in a freely selectable arrangement on a computer display screen. In most of these programs, the following interaction steps are required in order to carry out this task:                1. Adjust the desired partitioning of the display screen or display screens.        2. Select a sub-window, for example, via activation of the window with the mouse pointer.        3. Select the images to be displayed in this sub-window, for example, via a command to open the desired image.        
Steps 2 and 3 must be repeated at this point for each image to be displayed. An alternative solution uses the well-known “Drag-and-Drop” technique to display the individual images in the respective windows. For this, an overview window is provided that contains a list of all available images. The individual images are represented in this list by their name or a symbolic representation. For each image to be displayed, the corresponding element of this list is clicked with a mouse, dragged to the desired window and “dropped” there.
Both of these solutions have the disadvantage that the mouse pointer must cover a long distance over the display screen or display screens, which can present significant interaction complexity with large monitors. Furthermore, the step of opening an image in the first solution is combined with further mouse clicks and interaction steps that additionally delay the user.
A further disadvantage is that it is not immediately obvious which image is to be displayed in which window. Furthermore, systems that are not tailored for radiological applications frequently do not have the ability to quickly partition the display screen into the routinely used one, two or four sub-windows. Instead, the respective partitioning must be manually performed by opening and arranging the individual windows.
A solution that is tailored to the requirements of digital mammogram screenings is described in U.S. Pat. No. 6,243,095 B1. Therein all available images (usually eight) are put out in a fixed arrangement in a navigation window that shows symbolic indicators of the individual images. The user moves a mouse pointer over the navigation window in order to select an image to be displayed. As soon as the pointer is located over a symbol that is associated with an image, the corresponding image is displayed in one of the monitors. Two mouse clicks can be additionally used to switch between different resolution modes so that the display of two or four images on one monitor is also possible.
With these displays, however, only images that are adjacent in a preconfigured arrangement in the navigation window can be simultaneously displayed on a monitor. In addition, it is assumed that the same images are available in all cases, which may not be true. Therefore, these solutions offer only very limited flexibility.
The known solutions all have one or more of the following disadvantages:                The screening analysis usually use display screen partitioning into one or more sub-windows that is not fast and conveniently achieved.        The selection of a sub-window in which to display an image requires moving the mouse to the respective sub-window, which entails a long mouse movement because of the size of the monitor.        The selection of an image for display in a sub-window requires to much interaction complexity.        The user has no quick overview of which image is open in a specific window, and also, in which window a particular image is open.        The images can not be arbitrarily distributed in the display window, rather they are made available according to specified configurations.        It is presupposed that for each case the same set of images remain available.        